It has been widely practiced to prepare a mortar by admixing together a powder of hydraulic compound such as cement and plaster, water and a fine aggregate such as sand and also to prepare a concrete by utilizing a coarse aggregate such as gravel as well as these ingredients. However, a fresh or liquid concrete or mortar prepared by the conventional method can not manifest uniform property or characteristics (e.g., segregation, bleeding, fluidability). More particularly, even when the same kind of hydraulic compound and fine aggregate are used in the same quantities and the same quantity of water is added in the same manner to a mixture of the hydraulic compound and fine aggregate, the characteristics of the resulting fresh mixture will be greatly varied in each case, which would be caused by the fact that a quantity and state of water adhered to the surface of the fine aggregate thus used be respectively varied.
Consequently, in the preparation of mortar or concrete it is essential to determine the quantity and state of the surface water of the fine aggregate. For this purpose it has been considered that the quantity and state of the surface water of the aggregate should be measured in accordance with JIS (Japanese Industrial Standards) A1109 entitled "Method of Test for Specific Gravity and Water Absorption of Fine Aggregate". According to this method, by poking operation with a stick (340.+-.15 g weight, 25.+-.5 mm diameter) a test sample of fine aggregate is filled up into a metallic flow corn having inner diameters of 38 mm at the top and 89 mm at the bottom respectively and 74 mm height, and the flow corn thus filled with the fine aggregate is placed on a horizontal base and then drawn up. The fine aggregate is defined as being in an interstice-water saturated and surface-dry condition, when the corn-shaped accumulation of fine aggregate is firstly destroyed or slumped down. It is a conventional thought that in this condition the interstice of fine aggregate is saturated with water while the surface is substantially dry and that the water content of the fine aggregate in this condition determined by the method of JIS A1109 does not influence the characteristics of the resulting mortar or concrete and therefore can be disregarded in determination of total quantity of water necessary to prepare mortar or concrete. Thus, where the percentage of water contained in or adhered to the fine aggregate which must be taken into consideration in determination of the water quantity necessary for preparing mortar or concrete is hereby defined as "effective water percentage" and in turn the percentage of water which may be excluded from the necessary water quantity is defined as "ineffective water percentage", it has been recognized that the water percentage of the fine aggregate in a saturated surface-dry condition as determined by JIS A1109 (hereinafter called "JIS surface-dry water percentage") will be equal to the ineffective water percentage. However, as a result of our careful investigation it has been found that such a conventional recognition is not correct so that if mortar or concrete prepared according to the conventional recognition could not provide uniform characteristics.
Meanwhile, we have already proposed an epoch-making process of preparing mortar or concrete which is disclosed in Japanese Laid Open Patent No. 104958/1980 and U.S. Pat. No. 4,299,633 wherein the necessary water quantity is divided into two portions, namely primary water is incorporated with fine aggregate and cement followed by first kneading operation and then secondary water (and additives, if necessary) is added to the resulting mixture followed by second kneading operation. It has been confirmed that this method is capable of manufacturing mortar or concrete with a sufficient mechanical strength and constant properties. In order to achieve such advantageous results, however, this method will require that a water quantity adhered to the fine aggregate itself be accurately determined and adjusted to a certain value, which has been difficult according to the prior art method described before.
Accordingly an object of the invention is to clarify the influence of the quantity and/or percentage of water adhered to a fine aggregate to be used in preparation of mortar or concrete upon characteristics of a resulting mortar or concrete, and thereby providing a method of preparing mortar or concrete having improved and uniform characteristics.
Another object of the invention is to provide a novel method and device capable of definitely measuring a percentage of water adhered to a fine aggregate to be used in preparation of mortar or concrete.